Pub Date : 2020-02-05DOI: 10.3952/physics.v60i1.4166
A. Laurikėnas, K. Mažeika, D. Baltrunas, R. Skaudžius, A. Beganskiene, A. Kareiva
In this study for the synthesis of a hybrid organic-inorganic Fe3O(TFBDC)3(H2O)3·(DMF)3 compound a slow evaporation method has been suggested. THe synthesis product was characterized using X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) coupled with SEM and electron paramagnetic resonance (EPR) spectroscopy. THe antiferromagnetic/weakly ferromagnetic behaviour of the synthesized sample was confirmed by magnetization measurements and Mössbauer spectroscopy. THe synthesized magnetic material could be itself tested for different medical applications and could be used as precursor material for the preparation of nanostructured iron oxides with a variety of useful properties for biomedicine.
{"title":"Hybrid organic-inorganic Fe3O(TFBDC)3(H2O)3·(DMF)3 compound synthesized by slow evaporation method: Characterization and comparison of magnetic properties","authors":"A. Laurikėnas, K. Mažeika, D. Baltrunas, R. Skaudžius, A. Beganskiene, A. Kareiva","doi":"10.3952/physics.v60i1.4166","DOIUrl":"https://doi.org/10.3952/physics.v60i1.4166","url":null,"abstract":"In this study for the synthesis of a hybrid organic-inorganic Fe3O(TFBDC)3(H2O)3·(DMF)3 compound a slow evaporation method has been suggested. THe synthesis product was characterized using X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) coupled with SEM and electron paramagnetic resonance (EPR) spectroscopy. THe antiferromagnetic/weakly ferromagnetic behaviour of the synthesized sample was confirmed by magnetization measurements and Mössbauer spectroscopy. THe synthesized magnetic material could be itself tested for different medical applications and could be used as precursor material for the preparation of nanostructured iron oxides with a variety of useful properties for biomedicine.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"60 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2020-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41443939","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-02-05DOI: 10.3952/physics.v60i1.4165
B. Vengalis, A. Maneikis, G. Grigaliūnaitė-Vonsevičienė, R. Juškėnas, A. Selskis
The Co2MnSi (CMS) Heusler alloy films with thickness d = 90 ÷ 110 nm were grown by DC magnetron sputtering on both nonheated and heated Si(100) and MgO(100) substrates. The films grown (annealed) at T ≥ 400°C demonstrated a nanocrystalline structure with a partially ordered B2 phase and traces of a highly ordered L21 phase as found from XRD measurements. The films deposited onto the nonheated substrates followed by annealing at Tann = 300 ÷ 500°C demonstrated a gradual increase of the saturation magnetisation, Msat, up to about 4.0 μB/f.u. (at 295 K) while the coercity field, Hc, of the films increased from about 10 to 12 kA/m with Tann increasing from 400 to 500°C. Unusually low Hc values of about 0.1 and 0.3 kA/m have been indicated for the films grown in situ at 400°C on MgO and Si, respectively. A significant increase of the Hc values found for the films grown in situ at Ts = 450°C and reduced Msat values for similar films grown at 500°C have been associated with the instability of the ordered L21 structure at high temperatures.
{"title":"Alternating current susceptibility and magnetisation of nanocrystalline Co2MnSi Heusler alloy films","authors":"B. Vengalis, A. Maneikis, G. Grigaliūnaitė-Vonsevičienė, R. Juškėnas, A. Selskis","doi":"10.3952/physics.v60i1.4165","DOIUrl":"https://doi.org/10.3952/physics.v60i1.4165","url":null,"abstract":"The Co2MnSi (CMS) Heusler alloy films with thickness d = 90 ÷ 110 nm were grown by DC magnetron sputtering on both nonheated and heated Si(100) and MgO(100) substrates. The films grown (annealed) at T ≥ 400°C demonstrated a nanocrystalline structure with a partially ordered B2 phase and traces of a highly ordered L21 phase as found from XRD measurements. The films deposited onto the nonheated substrates followed by annealing at Tann = 300 ÷ 500°C demonstrated a gradual increase of the saturation magnetisation, Msat, up to about 4.0 μB/f.u. (at 295 K) while the coercity field, Hc, of the films increased from about 10 to 12 kA/m with Tann increasing from 400 to 500°C. Unusually low Hc values of about 0.1 and 0.3 kA/m have been indicated for the films grown in situ at 400°C on MgO and Si, respectively. A significant increase of the Hc values found for the films grown in situ at Ts = 450°C and reduced Msat values for similar films grown at 500°C have been associated with the instability of the ordered L21 structure at high temperatures.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2020-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48944594","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-02-05DOI: 10.3952/physics.v60i1.4160
V. Gulbinas
Charge carrier mobility in organic semiconductors is not a constant value unambigously characterizing some particular material, but depends on the electric field, temperature and even on time after it was generated or injected. The time dependence is particularly important for the thin-film devices where charge carriers pass the organic layer before mobility reaching its stationary value. Here we give a review of experimental techniques with ultrafast timeresolution enabling one to address the mobility kinetics and analyse properties of the time-dependent mobility in conjugated polymers and organic solar cells. We analyse kinetics during the charge carrier generation and extraction of free charge carriers. The mobility typically decreases by several orders of magnitude on a picosecond-nanosecond time scale; however, its kinetics also depends on the investigation technique. The mobility kinetics in blends for bulk heterojunction solar cells strongly depends on the stoichiometric ratio of donor and acceptor materials.
{"title":"Charge carrier mobility dynamics in organic semiconductors and solar cells","authors":"V. Gulbinas","doi":"10.3952/physics.v60i1.4160","DOIUrl":"https://doi.org/10.3952/physics.v60i1.4160","url":null,"abstract":"Charge carrier mobility in organic semiconductors is not a constant value unambigously characterizing some particular material, but depends on the electric field, temperature and even on time after it was generated or injected. The time dependence is particularly important for the thin-film devices where charge carriers pass the organic layer before mobility reaching its stationary value. Here we give a review of experimental techniques with ultrafast timeresolution enabling one to address the mobility kinetics and analyse properties of the time-dependent mobility in conjugated polymers and organic solar cells. We analyse kinetics during the charge carrier generation and extraction of free charge carriers. The mobility typically decreases by several orders of magnitude on a picosecond-nanosecond time scale; however, its kinetics also depends on the investigation technique. The mobility kinetics in blends for bulk heterojunction solar cells strongly depends on the stoichiometric ratio of donor and acceptor materials.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2020-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44808708","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-02-05DOI: 10.3952/physics.v60i1.4163
L. Ardaravičius, O. Kiprijanovič, M. Ramonas, E. Šermukšnis, A. Simukovic, A. Matulionis
High-field electron transport measurements by applying short (few ns) voltage pulses on nominally undoped n-type Zn-polar ZnO epilayers are reported and interpreted in terms of the Boltzmann kinetic equation. The transient measurements do not demonstrate a significant change in the electron density up to 320 kV/cm electric field. This result together with the experimental data on the current allows one to estimate the electron drift velocity from the measured current: the highest value of ~2.9 × 107 cm/s is obtained at the pre-breakdown field of 320 kV/cm for the ZnO layer with the electron density of 1.5 × 1017 cm–3. The densities of double-charged oxygen vacancies (~1.6 × 1017 cm–3) and other charged centres (~1.7 × 1017 cm–3) are assumed for the best fit of the simulated and measured hot-electron effect. A correlation with the epilayer growth conditions is demonstrated: the higher Zn cell temperature favours the formation of a higher density of the oxygen vacancies (1.9 × 1017 cm–3 at 347°C).
{"title":"Estimation of the charged defect density from hot-electron transport studies in epitaxial ZnO","authors":"L. Ardaravičius, O. Kiprijanovič, M. Ramonas, E. Šermukšnis, A. Simukovic, A. Matulionis","doi":"10.3952/physics.v60i1.4163","DOIUrl":"https://doi.org/10.3952/physics.v60i1.4163","url":null,"abstract":"High-field electron transport measurements by applying short (few ns) voltage pulses on nominally undoped n-type Zn-polar ZnO epilayers are reported and interpreted in terms of the Boltzmann kinetic equation. The transient measurements do not demonstrate a significant change in the electron density up to 320 kV/cm electric field. This result together with the experimental data on the current allows one to estimate the electron drift velocity from the measured current: the highest value of ~2.9 × 107 cm/s is obtained at the pre-breakdown field of 320 kV/cm for the ZnO layer with the electron density of 1.5 × 1017 cm–3. The densities of double-charged oxygen vacancies (~1.6 × 1017 cm–3) and other charged centres (~1.7 × 1017 cm–3) are assumed for the best fit of the simulated and measured hot-electron effect. A correlation with the epilayer growth conditions is demonstrated: the higher Zn cell temperature favours the formation of a higher density of the oxygen vacancies (1.9 × 1017 cm–3 at 347°C).","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2020-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42731167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-05DOI: 10.3952/physics.v59i4.4134
A. Hospodková, M. Zíková, T. Hubáček, J. Pangrác, K. Kuldová, F. Hájek, F. Dominec, A. Vetushka, S. Hasenöhrl
In this work the mechanism which helps to reduce the dislocation density by deposition of a SiNx interlayer is discussed. It is shown that the dislocation reduction by SiNx interlayer deposition is influenced by dislocation density in the underlying GaN layers. The SiNx interlayer is very effective when the original dislocation density is high, while in the case of lower dislocation density the deposition of SiNx is not effective for crystal quality improvement. Although it is widely accepted that SiNx serves as a barrier for dislocation propagation, similarly to the enhanced lateral overgrowth method, it is shown that after masking the SiNx deposition cannot be the dominant dislocation reduction mechanism. The most probable mechanism is the annihilation of bended neighbouring dislocations during the coalescence of 3D islands. The SiNx layer cannot serve as a barrier for dislocations, since it is probably dissolved during the following GaN growth and dissolved Si atoms are incorporated into the above-grown GaN layer which stimulates the 3D island formation. Then the use of the SiNx interlayer for dislocation reduction is recommended only for the improvement of layers with a high dislocation density. On the other hand, the PL signal was strongly enhanced for both low and high dislocation density structures with the SiNx interlayer, suggesting that the interlayer might help to suppress the nonradiative recombination in subsequent GaN that is not related to the dislocation density, which remained the same. But its origin has to be studied further.
{"title":"Improvement of GaN crystalline quality by SiNx layer grown by MOVPE","authors":"A. Hospodková, M. Zíková, T. Hubáček, J. Pangrác, K. Kuldová, F. Hájek, F. Dominec, A. Vetushka, S. Hasenöhrl","doi":"10.3952/physics.v59i4.4134","DOIUrl":"https://doi.org/10.3952/physics.v59i4.4134","url":null,"abstract":"In this work the mechanism which helps to reduce the dislocation density by deposition of a SiNx interlayer is discussed. It is shown that the dislocation reduction by SiNx interlayer deposition is influenced by dislocation density in the underlying GaN layers. The SiNx interlayer is very effective when the original dislocation density is high, while in the case of lower dislocation density the deposition of SiNx is not effective for crystal quality improvement. Although it is widely accepted that SiNx serves as a barrier for dislocation propagation, similarly to the enhanced lateral overgrowth method, it is shown that after masking the SiNx deposition cannot be the dominant dislocation reduction mechanism. The most probable mechanism is the annihilation of bended neighbouring dislocations during the coalescence of 3D islands. The SiNx layer cannot serve as a barrier for dislocations, since it is probably dissolved during the following GaN growth and dissolved Si atoms are incorporated into the above-grown GaN layer which stimulates the 3D island formation. Then the use of the SiNx interlayer for dislocation reduction is recommended only for the improvement of layers with a high dislocation density. On the other hand, the PL signal was strongly enhanced for both low and high dislocation density structures with the SiNx interlayer, suggesting that the interlayer might help to suppress the nonradiative recombination in subsequent GaN that is not related to the dislocation density, which remained the same. But its origin has to be studied further.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2020-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47617216","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-05DOI: 10.3952/physics.v59i4.4133
J. Novák, P. Eliáš, S. Hasenöhrl, A. Laurenčíková, P. Urbancová, D. Pudiš
Reduction and limitation of free spaces between the gallium phosphide nanocones was studied. A set of nanocone samples was grown by metal organic vapour phase epitaxy (MOVPE) in the temperature range between 610 and 690°C. Our results showed that by an appropriate combination of a high density of gold seeds and an optimized growth temperature it was possible to obtain a nanostructured surface with very limited free spaces between the nanocones. A combination of lateral and vertical growth rates regulated by the selection of growth temperature played a very important role in the nanocone hexagonal base enlargement, which helped to minimize spaces between the cones. The limitation of free space between the nanocones increased a probability of edge creation that is very helpful for the successful growth of 2D materials.
{"title":"Nanocone structures with limited interspace grown by MOVPE","authors":"J. Novák, P. Eliáš, S. Hasenöhrl, A. Laurenčíková, P. Urbancová, D. Pudiš","doi":"10.3952/physics.v59i4.4133","DOIUrl":"https://doi.org/10.3952/physics.v59i4.4133","url":null,"abstract":"Reduction and limitation of free spaces between the gallium phosphide nanocones was studied. A set of nanocone samples was grown by metal organic vapour phase epitaxy (MOVPE) in the temperature range between 610 and 690°C. Our results showed that by an appropriate combination of a high density of gold seeds and an optimized growth temperature it was possible to obtain a nanostructured surface with very limited free spaces between the nanocones. A combination of lateral and vertical growth rates regulated by the selection of growth temperature played a very important role in the nanocone hexagonal base enlargement, which helped to minimize spaces between the cones. The limitation of free space between the nanocones increased a probability of edge creation that is very helpful for the successful growth of 2D materials.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2020-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48307345","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-05DOI: 10.3952/physics.v59i4.4137
J. Pavlov, T. Ceponis, L. Deveikis, Tanja Heikkinen, Jyrki Raisanen, V. Rumbauskas, G. Tamulaitis, F. Tuomisto, E. Gaubas
In this work, pulsed photoionization as well as photoluminescence and positron annihilation spectroscopy were combined to detect different species of defects. The GaN crystals, grown by the ammono-thermal method, doped with Mn as well as Mg impurities and irradiated with different fluences of reactor neutrons, were examined to clarify the role of the technological and radiation defects. The evolution of the prevailing photoactive centres was examined by pulsed photoionization spectroscopy. Positron annihilation spectroscopy was applied to reveal vacancy-type defects.
{"title":"Spectroscopy of defects in neutron irradiated ammono-thermal GaN by combining photoionization, photoluminescence and positron annihilation techniques","authors":"J. Pavlov, T. Ceponis, L. Deveikis, Tanja Heikkinen, Jyrki Raisanen, V. Rumbauskas, G. Tamulaitis, F. Tuomisto, E. Gaubas","doi":"10.3952/physics.v59i4.4137","DOIUrl":"https://doi.org/10.3952/physics.v59i4.4137","url":null,"abstract":"In this work, pulsed photoionization as well as photoluminescence and positron annihilation spectroscopy were combined to detect different species of defects. The GaN crystals, grown by the ammono-thermal method, doped with Mn as well as Mg impurities and irradiated with different fluences of reactor neutrons, were examined to clarify the role of the technological and radiation defects. The evolution of the prevailing photoactive centres was examined by pulsed photoionization spectroscopy. Positron annihilation spectroscopy was applied to reveal vacancy-type defects.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2020-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46625777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-05DOI: 10.3952/physics.v59i4.4136
P. Kuznetsov, G. Yakushcheva, E. Savelyev, V. Yapaskurt, V. Shcherbakov, Alexey Temiryasev, L. Zakharov, V. A. Jitov, D. Sudas
Metal organic chemical vapour deposition (MOCVD) technology is adapted for the deposition of thin zinc and bismuth chalcogenides films on the surface of silica optical fibres with short tapered sections. Growth runs were carried out in a special tubular quartz reactor at atmospheric pressure of hydrogen at 425°C temperature using ZnEt2, BiMe3, Et2Te and i-Pro2Se as organometallic precursors. During the deposition of chalcogenides, the transmittance spectra of the fibre were recorded in regular short time intervals. In the transmittance spectra of the fibre with a tapered section coated by ZnSe and ZnTe, lossy mode resonances (LMR) were observed at a diameter of the tapered waist below 30 μm. After the deposition of very thin Bi2Te3 and Bi2Se3 island films on the tapered waist with a diameter about 10 μm optical fibres were built into erbium fibre ring lasers. A pulsed generation mode was achieved in some of lasers due to resonator Q-factor modulation. These results can be applied for the design of LMR fibre sensors and passively Q-switch pulsed fibre lasers.
{"title":"MOCVD deposition of zinc and bismuth chalcogenides films on the surface of silica optical fibres","authors":"P. Kuznetsov, G. Yakushcheva, E. Savelyev, V. Yapaskurt, V. Shcherbakov, Alexey Temiryasev, L. Zakharov, V. A. Jitov, D. Sudas","doi":"10.3952/physics.v59i4.4136","DOIUrl":"https://doi.org/10.3952/physics.v59i4.4136","url":null,"abstract":"Metal organic chemical vapour deposition (MOCVD) technology is adapted for the deposition of thin zinc and bismuth chalcogenides films on the surface of silica optical fibres with short tapered sections. Growth runs were carried out in a special tubular quartz reactor at atmospheric pressure of hydrogen at 425°C temperature using ZnEt2, BiMe3, Et2Te and i-Pro2Se as organometallic precursors. During the deposition of chalcogenides, the transmittance spectra of the fibre were recorded in regular short time intervals. In the transmittance spectra of the fibre with a tapered section coated by ZnSe and ZnTe, lossy mode resonances (LMR) were observed at a diameter of the tapered waist below 30 μm. After the deposition of very thin Bi2Te3 and Bi2Se3 island films on the tapered waist with a diameter about 10 μm optical fibres were built into erbium fibre ring lasers. A pulsed generation mode was achieved in some of lasers due to resonator Q-factor modulation. These results can be applied for the design of LMR fibre sensors and passively Q-switch pulsed fibre lasers.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":"59 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2020-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45701236","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-05DOI: 10.3952/physics.v59i4.4135
N. Tillner, C. Brandl, M. Hoffmann, R. Moser, A. Waag, H. Lugauer
Conventional aluminum nitride (AlN) template fabrication techniques, like hydride vapour phase epitaxy or AlN growth on patterned sapphire substrates, usually lead to step-bunched template surfaces. The resulting macrosteps cause emission broadening or even multiple-peak characteristics of ultraviolet light-emitting diodes (UV LEDs) fabricated on such AlN templates. In order to reduce these macrosteps and to provide a smoother surface, even without the need of a thick AlN deposition, a two-layer growth procedure is reported here. A three-dimensional (3D) – twodimensional (2D) sequential growth initiates a significant modification of the previous AlN surface morphology and simultaneously limits the evolving tensile strain. A primarily step-bunched surface with a surface roughness root mean square of 1.8 nm is successfully reduced by the two-layer growth procedure down to 0.8 nm, without any film cracking. This distinct roughness reduction of more than 50% is achieved within an AlN thickness of only 1.3 μm. With a smoother surface, the electroluminescence characteristic of a UV LED structure is substantially improved. Instead of a double-peak emission, typical for LEDs grown on step-bunched templates, a single-peak emission and lower spectral width were achieved, indicating the high potential of the suggested two-layer technique for improving performance.
{"title":"Reduction of surface roughness by modification of step-bunched aluminum nitride layers towards step-flow morphology","authors":"N. Tillner, C. Brandl, M. Hoffmann, R. Moser, A. Waag, H. Lugauer","doi":"10.3952/physics.v59i4.4135","DOIUrl":"https://doi.org/10.3952/physics.v59i4.4135","url":null,"abstract":"Conventional aluminum nitride (AlN) template fabrication techniques, like hydride vapour phase epitaxy or AlN growth on patterned sapphire substrates, usually lead to step-bunched template surfaces. The resulting macrosteps cause emission broadening or even multiple-peak characteristics of ultraviolet light-emitting diodes (UV LEDs) fabricated on such AlN templates. In order to reduce these macrosteps and to provide a smoother surface, even without the need of a thick AlN deposition, a two-layer growth procedure is reported here. A three-dimensional (3D) – twodimensional (2D) sequential growth initiates a significant modification of the previous AlN surface morphology and simultaneously limits the evolving tensile strain. A primarily step-bunched surface with a surface roughness root mean square of 1.8 nm is successfully reduced by the two-layer growth procedure down to 0.8 nm, without any film cracking. This distinct roughness reduction of more than 50% is achieved within an AlN thickness of only 1.3 μm. With a smoother surface, the electroluminescence characteristic of a UV LED structure is substantially improved. Instead of a double-peak emission, typical for LEDs grown on step-bunched templates, a single-peak emission and lower spectral width were achieved, indicating the high potential of the suggested two-layer technique for improving performance.","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2020-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45719649","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-05DOI: 10.3952/physics.v59i4.4138
D. Adamchuk, V. Ksenevich, N. Poklonski, Marius Navickas, J. Banys
The work was supported by the State Committee on Science and Technology of the Republic of Belarus (Grant No. F19LITG-001), Research Council of Lithuania (Grant No. S-LB-19-5), Belarusian National Research Program ‘Convergence-2020’ (subprogram ‘Integration’, Grant No. 3.3.1), and by Program of EU H2020-MSCA-RISE-2015 (Grants No. 691010 HUNTER and No. 690968 NANOGUARD2Ar).
{"title":"Nonstoichiometric tin oxide films: study by X-ray diffraction, Raman scattering and electron paramagnetic resonance","authors":"D. Adamchuk, V. Ksenevich, N. Poklonski, Marius Navickas, J. Banys","doi":"10.3952/physics.v59i4.4138","DOIUrl":"https://doi.org/10.3952/physics.v59i4.4138","url":null,"abstract":"The work was supported by the State Committee on Science and Technology of the Republic of Belarus (Grant No. F19LITG-001), Research Council of Lithuania (Grant No. S-LB-19-5), Belarusian National Research Program ‘Convergence-2020’ (subprogram ‘Integration’, Grant No. 3.3.1), and by Program of EU H2020-MSCA-RISE-2015 (Grants No. 691010 HUNTER and No. 690968 NANOGUARD2Ar).","PeriodicalId":18144,"journal":{"name":"Lithuanian Journal of Physics","volume":" ","pages":""},"PeriodicalIF":0.6,"publicationDate":"2020-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48212208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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